The present invention relates generally to adaptive equalizers, and more particularly, to adaptive equalizers and processing methods that provide for adaptive equalization at very high data symbol rates.
A well-known technique for minimizing the effect of intersymbol interference is to "equalize" digitally modulated signals. Intersymbol interference is generated as a result of non-ideal phase and frequency characteristics of a transmitter, a receiver, and a communication channel therebetween. Such non-ideal channel characteristics result in various delays for different signal frequency components. The effect of intersymbol interference is that a particular received signal pulse will be distorted by late frequency components of previous pulses and early frequency components of successive pulses.
An equalizer receives some number of earlier pulses, a current pulse, and some number of later pulses. In an ideal situation, by suitably adding and subtracting suitably scaled received pulses to and from the current pulse, the effect of intersymbol interference at a particular sample time of a received pulse can be totally removed. In practical applications of this idea, the equalizer is designed to adapt to the phenomena that causes the intersymbol interference. The benefits of such an adaptive equalizer is that it is not necessary to model the entire communication chain, since it adapts to both fixed and time varying parameters, and in particular to the effect of a changing dispersive communication channel.
U.S. Pat. No. 4,759,037 issued to Debus, Jr. et al., describes an adaptive equalization technique for equalizing an incoming signal including quadrature-related carder signals by forming the product of the incoming signal at at least one prescribed time and only one real-valued coefficient associated with each time. In one embodiment the equalized incoming signal is demodulated into a first pair of component signals. At least one of these component signals is then used to generate each coefficient. In another embodiment each coefficient is generated in response to at least one of the component signals in the first pair along with a second pair or component signals which are formed by demodulating the incoming signals.